In machining a machine tool, much cutting fluid is supplied to the machining point to cool and lubricate a workpiece or a tool device, or to remove cutting chips. In this case, there happen many problems such as environmental pollution and a bad influence to human health due to cutting fluid, a big cost accompanying waste oil disposal of the cutting fluid, a decrease in the tool device life by cooling of the workpiece, and sliding wear of the tool device due to an excess of cutting fluid during fine cutting machining. In addition, because much cutting fluid adheres to the cutting chips during machining, the adhered cutting fluid must be removed from the cutting chips in treating or recycling.
To settle these problems, recently, a machine tool that carries out so-called dry cutting has appeared. The dry cutting is what cuts the machining point as supplying a very small quantity of atomized cutting fluid.
The applicant has already put in operation a machine tool that carries out the dry cutting. Here, a spindle device of the machine tool, as shown in FIG. 11, involves a tool holder 4 fixing a tool device 13 is on a spindle 1 through a taper-shank part 5b thereof.
In this case, a straight holder side atomized cutting fluid passage e2 having a single passage cross section is provided to the tool holder 4. The passage e2 comprises a central hole “d” of a pull-stud 6, an inner hole “f” of a holder inside connecting pipe 8 and a tool device inside passage “g” provided to the thickness of the tool device 13. Besides, a spindle side atomized cutting fluid passage e1 comprising an inner hole of an inner pipe 3 is provided to the spindle 1. Here, the inner pipe 3 is provided to a rotating center of the spindle 1, having a single passage cross section.
While the tool device is machining, atomized cutting fluid generated by an atomized cutting fluid generator provided near the spindle 1 is supplied to the base of the passage e1. Then, the atomized cutting fluid passes through the passage e1, thereafter spouting from the tip of the tool holder 13 through the passage e2.
In the above-mentioned conventional machine tool, the rotating speed of the spindle 1 varies according to the operating circumstance When the rotating speed becomes large, the centrifugal force acting on the atomized cutting fluid flowing inside the passages e1 and e2 increases. Therefore, the pressure of the atomized cutting fluid near the inner peripheral surface of the passages e1 and e2 ascends; thereby promoting the liquefaction thereof as well as inhibiting a stable supply thereof. Accordingly, there occur various bad influences such as a reduction in the tool device life and the machining surface quality.
While the machine tool operates, the supply of the atomized cutting fluid is frequently stopped and re-started to avoid a useless supply. When the supply is stopped, the atomized cutting fluid inside the passages e1 and e2 escapes instantly. Accordingly, when the supply of the atomized cutting fluid is restarted, unless the passages e1 and e2 are filled with the atomized cutting fluid, a stable supply circumference is not accomplished and efficient operation is also hindered.
The present invention aims to provide a spindle device of a machine tool that can settle the above-mentioned troubles.